MC-4177

Elmar observed a control-plane bug while supervising direct Codex tmux work: instructions were pasted into the Codex tmux session, but not submitted; he had to manually press Enter before Codex started. Impact: - Direct Codex tmux sessions can appear active in MC/runtime state while actually sitting idle at a pasted prompt. - This creates false progress claims and requires manual intervention from Elmar. Scope: - Investigate the Codex tmux/session launch path used by direct Codex runtime sessions, including MC ticket dispatch, runtime_sessions/tmux metadata, and any send-keys/paste/Enter handling. - Fix the launch/injection code so newly spawned Codex tmux sessions receive the prompt and an explicit Enter/submit reliably. - Add a regression test or narrow harness that proves the command path sends the terminal submit/Enter, not just paste text. - Verify with a harmless Codex/tmux smoke or equivalent fake tmux harness; do not require Elmar to press Enter. - Do not restart production :3001 unless the final deployment step requires it and is safe; use preview/test harnesses first. Expected check-in: 2026-05-25T14:26:44+02:00 Acceptance: - A newly started Codex tmux session begins executing without manual Enter. - Runtime/session ledger does not mark a worker active before the prompt is actually submitted. - Tests cover the paste+Enter behavior or the abstraction that performs it.